1. Field of the Invention
This invention relates to ceiling runners for a suspended ceiling system. More specifically it relates to a method of mechanically joining two strips of metal together. The method is well suited to be used within a high speed rollforming process. In addition, it will be disclosed that grid tee sections customarily manufactured through rollforming can be improved and made more efficient by use of this method.
2. Description of the Prior Art
To date many methods have been developed to mechanically fasten two layers of sheet metal together. Most methods require a series of press hits as per U.S. Pat. Nos. 3,083,794, 3,614,819 and 3,726,000. These methods require the material to be stationary and are not suited for close spacing in a fast moving manufacturing process such as rollforming.
U.S. Pat. No. 4,206,578 illustrates an earlier grid tee product with a second strip of metal fastened within the section. The method used in this product lances an ear on three sides and folds it through and around to achieve the mechanical attachment. A through opening is a result of this method. This opening would be unacceptable for product applications where routings and formed locks are to be applied to the section over the fastened areas.
U.S. Pat. No. 4,489,529 discloses a means to improve the rotational stiffness of a grid tee section through the application of a series of vertical lances along the base of the vertical web.
U.S. Pat. Nos. 3,284,873 and 3,726,000 disclose the use of punches to pierce two adjacent pieces of material to fasten the two pieces together. A commercial product of Eastern Products was similar to that of U.S. Pat. No. 3,726,000.
The new process invention can be used to provide a series of attached points along the vertical web, without vertical lances or piercing of metal as shown in the prior art, which will be more effective in improving rotational stiffness.